Preparation, Characterization And Application Of Nano Cellulose Fibrils From Bamboo

Nano-cellulose fibrils （NCF） and its composites own a lot of special physical andmechanical properties due to the unique chemical molecular structure and nano-size effect.This special material is very potential in the application of some important areas, such asadvanced materials, optoelectronic devices, packaging and pharmacy. In this paper, bamboowas for the first time taken as raw material to prepare NCF and its products, and the differencesfor preparing NCF by bamboo fibers or parenchyma cells were compared. Besides, based onindustrial prospects, the technology for preparing NCF was studied by taking commercialbamboo pulp and bamboo processing residues as raw materials. Finally, the preparation andproperty of NCF film, NCF aerogels and NCF/phenolic resin composites based on NCF solwere focused on and the potential application on bamboo-based NCF was also discussed.Both parenchyma cells and bamboo fibers after homogenization could be used to prepareNCF sol with high quality, but differences exist in the dissociation process. In thehomogenization process of bamboo fibers the four steps include the fiber segment, thedissociation of the fiber segment, the cell wall crushing, the separation of fiber bundles. Whilefor Parenchyma cells, there are only three steps including cell disruption, parietal dissociation,the separation of fiber bundles. Overall, the cell wall structure of bamboo fiber is very dense,which is responsible for high energy consumption and a lot of processes by using existingprocessing techniques. The efficiency of producing NCF could be improved by taking saturatedsalt solutions as a substitution for purified water to reduce the viscosity of the solution.NCF sol with high quality could be prepared by the use of high pressure homogenizationtechniques when taking industrial bamboo pulp as the raw material, while appropriatemechanical pretreatment is also essential. Homogenizing treatment with high speed couldinduce the strip of the outer cell wall, and then ultrasonic treatment plays a significant role inthe devillicate of bamboo fibers. The method which combines ultrasonic pretreatment withhigh-speed homogenizer is an effective way to avoid the inlet blockage and uneven crush before high-pressure homogenization. Swelling agent used as a method to pretreat bamboopulp could replace mechanical pretreatment, thereby reducing energy consumption forpreparing NCF.Parenchyma cells up to80%of bamboo processing residue is a good raw material, whichcould be used for preparing NCF after sieving and chemical pretreatment. Ultrasonic treatmentis a very suitable method to produce NCF by parenchyma cells, and parenchyma cells withchemical pretreatment could be prepared into excellent NCF sol by50-min ultrasonic treatment.Less than0.5wt%of solution concentration should be used because during the ultrasonicprocess high concentration may reduce the ultrasonic cavitation effect. For the parenchymacells, the ultrasonication and high pressure homogenization could both be used to prepare NCFsol, but in terms of parenchyma cell disruption, the ultrasonication is better, while thehigh-pressure homogenizing effect on the cell walls is more apparent.NCF film material with compact structure and excellent mechanical properties can beprepared by vacuum filtration. After40-min ultrasonic treatment, its physical and mechanicalproperties can be stable, and its modulus and strength were respectively12.6GPa and141MPa.The processing time, the film thickness, moisture content and other factors significantly affectthe mechanical properties of the material. By controlling the drying air flow direction and thedrying time NCF film with certain orientation can be prepared. Results show that there is adifference of about20%in the tensile strength and elastic modulus at the perpendiculardirection and in terms of creep and elongation at break for different directions, there aresignificant differences in performance.NCF aerogels with high toughness and very low density can be prepared by freeze drying,and the density of NCF aerogels could be as low as0.5×10^-3g/cm³, which is2.5times as thatof the world’s lightest solid material. The freezing method has a significant influence NCF onaerogel microstructure. Better NCF aerogels could be prepared by an ultra-low temperaturefreezer or liquid nitrogen. NCF aerogel material has excellent energy adsorption. Energyabsorption value of NCF aerogels with a density of10mg/cm³could be up to220kJ/m3, whichis very close to that of the polystyrene foam with5-time density. NCF bundles as a whole in NCF aerogels are arranged at random, but local NCF bundle orientation can be achieved byrapid freezing method.NCF/PF composite materials with low resin load ratio （PF content of less than15%）could be prepared using NCF aerogels made by concentration and freezing drying as a loadcarrier in phenolic resin. The strength and modulus of this composite material wererespectively150MPa and5GPa. This process can make the phenol resin uniformly distributein the composite material. At high humidity, hygroscopicity of NCF/PF composite material islower than that of pure NCF film material; besides, at the same moisture content, littledifference exists in the elastic modulus, breaking strength and elongation at break.